1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor element, and particularly to a method of manufacturing a nitride semiconductor laser element.
2. Discussion of the Related Art
A nitride semiconductor is formed by a compound semiconductor of InxAlyGa1-x-yN (0≦x, 0≦y, and 0≦x+y≦1), various demands for the semiconductor laser elements using such a nitride semiconductor have been increasing, for use in optical disc systems capable of recording and reproducing large-volume, high-density information such as a next-generation DVD, and for use in electric appliances such as personal computers. For this, many studies have been conducted to manufacture the semiconductor laser elements using such a nitride semiconductor with a good reproducibility while maintaining their stable properties.
For example, in order to prevent chipping and cracking of the ridge due to propagation from a dislocation-concentrated region upon forming a resonator surface by cleavage so as to reduce damage to a nitride semiconductor laser element and to stabilize a current-voltage characteristics of the element, there has been proposed is a method of forming grooves which extend in the resonator direction of the laser element and cut from an upper surface of nitride semiconductor growth layers into an interface of a p-n junction, as described in JP 2004-327879A.
However, even if cleavage is performed by using such grooves (as in JP 2004-327879A), cleaved planes may deviate from the intended locations due to dislocation density and crystal defects and the like within the substrate or nitride semiconductor layers, making it difficult to achieve a stable product yield
In the cases where partial grooves in a shape of dotted line, cross, and the like, are formed on the intended dividing lines by laser processing as described in JP2004-165226A, JP2004-165227A, and JP2004-259046A, a high precision is not required, because a wider width is allowed to the predetermined cleavage lines by using the surrounding area of an LED as a margin for cutting. On the other hand, this method cannot be applied to a high-precision dividing. In the cases where the predetermined cleavage lines are formed by typical scribing or by laser processing, cleavage locations may be contaminated, damaged, or deformed by scribing. Also, because of their large processing width and low precision, stable dividing with a repeatable degree of high precision cannot be obtained, so that such scribing is not applicable to divide the element regions.
In semiconductor laser elements, typically, a two-step dividing process is employed, in which a wafer is divided into bar-shaped pieces (hereinafter may be described as primary cleavage) and then a bar-shape semiconductor element is divided into chip-shaped pieces (hereinafter may be described as secondary cleavage). Thus, a resonator surface is formed by cleaving into bar-shape and an end-surface protective film is disposed on the resonator surface. That is, laser beam is emitted from the resonator surface formed by the primary cleavage. Therefore, high accuracy, in other word, a smooth resonator end surface is required to be formed in the primary cleavage.
There has been a method of dividing, in which cleaving property of the semiconductor substrate used to form a semiconductor element structure is used for dividing. However, cleavage may depend on the crystallinity of the substrate and it may cause difficulty in control of cleavage. For example, in a nitride semiconductor substrate whose substrate crystal is formed by growths of different in-plane crystal orientations, such as by ELO growth, controlling of cleavage becomes significantly difficult.